1. Field of the Invention
This invention relates to aluminum conductors of UHV transmission lines.
2. Prior Art
Oil or grease tends to adhere to the surface of aluminium conductors of UHV transmission lines during the manufacture thereof. If such a conductor is laid in the air, water drops, for a certain period of time, collect on the conductor surface during and immediately after a rainfall because of the presence of the oily material adhered to the conductor surface. As a result, the conductor surface gets wet unevenly. This gives rise to corona discharges which cause a great audible noise. This problem has been serious particularly in residential areas. Conventionally, the oily material is removed from the conductor surface, using cloth or the like, after the aluminum conductor is strung in the air in order to prevent the corona discharges, thereby reducing the audible noise. However, this procedure has been found not wholly satisfactory. In addition, it has proven to be quite difficult to remove the oily material from the conductor surface since this removing operation is carried out at locations high in the air.
It has been proposed in the art to treat the conductor surface so that water drops, collecting on the surface during and immediately after a rainfall, are caused to dissipate quickly, thereby causing the conductor surface to get wet uniformly. One such method is known from Japanese Patent Publication No. 36-14185 in which the surfaces of wires constituting a conductor are treated by sand blasting so that rain drops on the conductor surface are caused to disperse, thereby preventing rain drops of relatively large diameter from collecting on the conductor surface and also dissipating the rain water on the conductor surface. With this method, however, rain drops of small diameter are still present on the conductor surface, and as a result a satisfactory water dissipation is not achieved. Another method is known from Japanese Patent Publication No. 36-14076 in which a film of a hydrophilic compound having a hydroxyl group is coated on wires constituting a conductor so that the wettability of the conductor surface is enhanced to prevent the collection of rain drops thereon. With this method, however, the rain drops are caused to spread slowly over the conductor surface, and the extent of spreading of the rain drops is small. As a result, the conductor surface fails to get wet uniformly. Thus, the above-mentioned known methods have also been unsatisfactory in that the generation of audible noise is not fully prevented.